A casted block member can have a wet passage which contains pressurized fluid. It is therefore preferable that the material of such a block member have a low porosity to obstruct seepage of oil from the wet passage through the block member to its outer surface. It is particularly desirable that the block member have a low porosity in the region between the wet passage and the portion of the outer surface which is closest to the wet passage. This is due to this portion of the block member providing the shortest path between the wet passage and the outer surface.
When such a block member is casted, the skin of its outer surface which directly contacts the internally cooled die steel typically has a low porosity. This casted skin of the outer surface can be removed during machining o the outer surface to expose a surface which, prior to the machining, was unexposed. A portion of the block member which was unexposed. A portion of the block member which was unexposed during the casting process can have a higher porosity (and lower resistance to seepage through the block member) than a surface which directly contacted the die steel during casting. Thus, it is desirable to not remove the casted skin, particularly in the vicinity of the wet passage, since the casted skin increases resistance of the block member to oil seepage from the wet passage through the block member to the outer surface.